BMP, engine mismanagement or not?

With so much talk about the Big Mixture Pull,"BMP" and experts like Mike Bush,
as well as the good folks from APS advocating this kind of engine operating procedure, I decided to try out this old and now newly discovered engine management technique.
The gragh shows a one hour flight where I did everything I was tought not to do.
Based on what Mike Bush explains in the latest SA article I tried the following:
Full throttle, reduce RPM only "oversquare", BMP on climb out "1500 feet"
Climb out well lean of peak with Cylinder Head temperatures well below 380.
Mine dropped to less than 300 F but EGTs where much higher than on the rich side of peak. Fuel flow was about 5 GPH less than on the rich side of peak. The GAMI spread as calculated by the EG view software shows 0.00GPH
on this flight. All was done on mogasE10 which I have been using for almost a year now and avgas in the left tank only for take off and landing.
Looking at the numbers, I can't see anything wrong with my new technique.
High MP and low RPMs contribute to a much more quiet cockpit environment
and less friction loss apparently. The fuel savings are obvious and although my engine does not suffer from high temperatures of any kind, lower CHTs are even better.
Flame suit on,what do you think?

I haven't brought myself to do the BMP early and climb WOTLOP yet, but that's usually because I'm in a hurry (always, it seems) and want full power for climb and keep it rich enough to keep it cool, then pull it as soon as I level out.

Logically I know it would only cost me a couple minutes of additional flight time and save a fair bit of fuel by climbing LOP, I just don't do it. In an RV where climb airspeed is 100+ it makes more sense because you can keep the engine cool easily - but in my 172 (until I get my 9A flying!) that's not an option and I'm just scared of cooking a cylinder - so I continue to throw fuel at the problem.

Ernst, welcome to the LOP club. I have been doing this for 2+ years, with the blessing of Allan Barrett once I passed the 25 hour mark. I pull the plugs and borescope every cylinder with each oil change @ 25 hr interval. Did I mention that I am compulsive? Plugs, valves and pistons all look great. My home field elevation is 5800' so I am below 75% power almost as soon as I get off the ground, but I follow the same procedure when operating out of sea level fields. All of this was preceeded by 2 rounds of balancing my AFP injectors. and I routinely cruise at 10.9 GPH and WOT. When I first started running LOP I would do a slow pull, and it scared me to see CHT's climbing. Now I make the Big Pull in 2-3 seconds till I see 10.9 GPH fuel flow and leave it there.

Jim Berry
RV-10
Barrett XIO-540

Looks like 25" and 2250 RPM, LOP. Have your Lycoming O-540 power chart handy? I think you'll find this MP and RPM setting is on the safe side of the "Limiting Manifold Pressure For Continuous Operation" line. Factory approved, so to speak.

The chart assumes best power mixture, so LOP isn't a detonation concern on 100LL. The mogas is a wildcard. For sure lower octane means less detonation margin, but your CHT lines suggest you have enough.

I have tried LOP climbs at gross weight in the summer and preferred getting to 10,500-13,500 where we can get some air conditioning going sooner. I may try it again with winter flying and better engine/wing/prop performance.

I considered trying the BMP. I talked with the guys at ECI and they did a BMP with a engine in the test stand. On one attempt the engine experienced a immediate problem and had extensive damaged. They attributed it to the BMP and don't recommend it for ECI engines.

George

sailvi767 said:

I considered trying the BMP. I talked with the guys at ECI and they did a BMP with a engine in the test stand. On one attempt the engine experienced a immediate problem and had extensive damaged. They attributed it to the BMP and don't recommend it for ECI engines.

George

Click to expand...

At what power setting were they operating? 100% ? 75% ? 65% ? Without that info, this is anecdotal and means absolutely nothing - no conclusions can be drawn from the presented statement.

Thank you for the feed back.
I wish you could tell us more about this test stand damage.
Unfortunately it is this kind of information that rests in the back of my mind
and casts doubt on the BMP.
With precise details available to the pilot through advanced engine monitors
I am certain I would be able to spot a detonation event. Certainly CHTs anywhere near 380F would keep me from doing a BMP.

I considered trying the BMP. I talked with the guys at ECI and they did a BMP with a engine in the test stand. On one attempt the engine experienced a immediate problem and had extensive damaged. They attributed it to the BMP and don't recommend it for ECI engines.

Click to expand...

Jim

Jim B

Also hanger at KAPA. I will peek in to see your borescope image the next time I see your cowl off.

I do the 4 cylinder version of the big pull consistantly at 7500 feet - about the time takeoff/airport environment workload is dropping off. In my case, I pull to 6.8 gph on my little 320 (with AFP) after slowing the prop to 2500, and can typically leave the mixture alone all the way up to 12,500. It inches closer to peak EGT with the climb but stays at least 15 LOP.

Works at lower altitude too. Get off the ground about 1000 feet ROP, set prop to 2500, throttle manifold to 75%, pull the fuel flow to 6.8 and like clockwork - 50 LOP. Makes mixture management easy. Really cold to really hot weather only seems to make a 0.2 gph difference either way. I think AFP compensates for altitude density to some degree.

As a proportion of rated horsepower, I should be pulling to 6.7 gph, (10.9*160/260) so we are really close.

I put in 9:1 pistons about 700 hours ago. No issures.

Little BMP

Jim B

Also hanger at KAPA. I will peek in to see your borescope image the next time I see your cowl off.

I do the 4 cylinder version of the big pull consistantly at 7500 feet - about the time takeoff/airport environment workload is dropping off. In my case, I pull to 6.8 gph on my little 320 (with AFP) after slowing the prop to 2500, and can typically leave the mixture alone all the way up to 12,500. It inches closer to peak EGT with the climb but stays at least 15 LOP.

Works at lower altitude too. Get off the ground about 1000 feet ROP, set prop to 2500, throttle manifold to 75%, pull the fuel flow to 6.8 and like clockwork - 50 LOP. Makes mixture management easy. Really cold to really hot weather only seems to make a 0.2 gph difference either way. I think AFP compensates for altitude density to some degree.

As a proportion of rated horsepower, I should be pulling to 6.7 gph, (10.9*160/260) so we are really close.

I put in 9:1 pistons about 700 hours ago. No issures.

Duane,

I will need to do an oil change in about 5 more hours, which may be delayed by my wife's knee replacement next week. Should have a new dental scope by then, so the screen resolution will be improved. I have the 9:1 pistons and roller cam in my XIO-540. See you soon.

Jim Berry
RV-10

Ironflight said:

At what power setting were they operating? 100% ? 75% ? 65% ? Without that info, this is anecdotal and means absolutely nothing - no conclusions can be drawn from the presented statement.

Click to expand...

I wish I had the data you mention however I don't have access to the actual conditions. Here is a link to the ECI service bulletin. It is certainly not definitive however it was enough to keep me from trying the technique.

http://www.eci.aero/pdf/93-6-7.pdf




George

N15JB said:

....Now I make the Big Pull in 2-3 seconds till I see 10.9 GPH fuel flow and leave it there.

Click to expand...

This is entirely consistent with my experience with a carbureted Continental O-470 in my Cessna 180, flying out of Longmont. Except that for this slightly smaller engine, the fuel flow is slightly lower, pretty much in proportion to the displacement.

The only thing worth adding is that if I fly much richer than that the valves start to stick on start-up. The engine is happier relatively lean than relatively rich, especially at low power.

Dave

ECI report

The ECI report is quite sobering, especially in light of the fact they were not able to detect a detonation event on their sophisticated engine monitoring equipment.
There is no doubt, EGT's rise rapidly during a BMP and may cause damage.
I also know of other anecdotal reports coming from engine overhaul shops
who claim to know what kind of engine monitoring equipment is installed just by looking at the cylinders and pistons. That being evidence of rapid heating and cooling events due to using fuel flow information to lean engines.
I was under the impression that I was able see what is going on inside the cylinders by closely monitoring temperatures but the ECI report shoots that idea full of holes.

I have read everything I can find on how to lean and run a piston engine since prior to buying my RV6 I had limited as in no experience with piston aircraft engines. There is a lot of conflicting information out there. One of the things that may contribute to those conflicts is lumping turbo or supercharged engines in with regular engines. Much of the data is geared toward the turbo 540's. It may well be that there is a significant difference in how the cylinders and pistons cool and heat up in a boosted verses a non boosted engine. Perhaps someone with more experience can comment on that. That could mean that a BMP is fine on a boosted engine but not so fine on a non boosted engine.

George

The ECI document is a Service Instruction from 1993. Engine monitors have come a long way since then and LOP operations, including the big mixture pull, are pretty much mainstream operational procedures, especially in our experimental world. This all seems like a bunch of hooey. BMP has worked fine for me.

erich

Nice catch on the 1993. There is little hard data in the ECI report, so it is hard to take it too seriously. However, I can see the potential risk of shock cooling by mixture alone. Normally, i think of shock cooling by rapid throttle movement, but the mixture control could do the same effective thing.

In an extreme case, you could go from a high power setting to mixture cut-off and that would certainly be a bad thing to do.

I will probalby tweak my takeoff to climb procedure a bit given the above to minimize any risk of cooling the engine too rapidly.

LOP lowers CHT

N427EF said:

Thank you for the feed back.
I wish you could tell us more about this test stand damage.
Unfortunately it is this kind of information that rests in the back of my mind
and casts doubt on the BMP.
With precise details available to the pilot through advanced engine monitors
I am certain I would be able to spot a detonation event. Certainly CHTs anywhere near 380F would keep me from doing a BMP.

Click to expand...

Having flown over 1000 hours in the Lean Of Peak (LOP) world, CHT's of 380 while rich of peak (ROP) would actually come down quite nicely LOP. I would be more worried about detonation with CHT's 380 ROP than CHT's 380 and LOP... but at 65% I usually saw highest CHT's around 360-350 LOP.

I went to the trouble of emailing Mike Busch and asking his opinion on the the ECI rapid leaning service instruction cited in a previous post. For those who value his opinion, here was his reply:

"Personally, I think the ECi SI is misguided. Whoever wrote it equated rapid leaning with rapid CHT change. Rapid CHT change is not a good thing, but a properly executed "big mixture pull" going from quite ROP to quite LOP will not result in a rapid CHT change and will not hurt anything. (Doing the BMP slowly will definitely hurt things.) If doing a rapid BMP was harmful, explain to me why my engines are both at 200%+ of TBO and 9 of my 12 cylinders are at 4700 hours total time in service."

Makes sense to me. I certainly don't see rapid drops in CHTs when doing the big pull.
Erich

erich weaver said:

"Personally, I think the ECi SI is misguided. Whoever wrote it equated rapid leaning with rapid CHT change. Rapid CHT change is not a good thing, but a properly executed "big mixture pull" going from quite ROP to quite LOP will not result in a rapid CHT change and will not hurt anything. (Doing the BMP slowly will definitely hurt things.)"

Click to expand...

I too think the SI is misguided on several fronts. However, in fairness, nowhere does the SI equate rapid leaning with rapid CHT change. The expressed concern is a rapid increase of piston diameter without time for a matching increase in cylinder diameter, with cylinder/piston scuffing as a result.

The expressed concern is a rapid increase of piston diameter without time for a matching increase in cylinder diameter, with cylinder/piston scuffing as a result.

Click to expand...

Precisely my concern after reading the ECI report.
Just to be sure, no one is advocating a slow BMP. It's either a BMP or traditional gradual leaning staying on the rich side for climb and once level in cruise at around 65% power again gradually leaning over to LOP.
I was doing my BMP at 1500 feet with 85% power and CHTs in the 320 and dropping after the BMP but as I pointed out EGTs rise instantly and this is consistent with the concern expressed in the ECI report.
No one says EGTs of 1400 degrees is a bad thing but going from 1180 to 1400
in less than 2 seconds is maybe what worries me a bit.

The kings of LOP are the APS folks in Ada, OK. The only issues in the old world about running LOP was that the fuel injectors might have been mismatched and the pilot thinking he was lean was actually slightly ROP.

I have always run my engines LOP and not only does it generally extend the life between overhauls. As in this thread the naysayers say "i heard from a friend" etc but never show any scientific proof to back what they are saying.

Net net if you have the time hit up George Braly or Walter Atkinson in person or take one of their online courses. Please do not propagate the anti-LOP nonsense

I don't think this is a anti LOP thread. The discussion is about the BMP as a method to get there.

George

BMP at Take off Power

I don't think this is a anti LOP thread. The discussion is about the BMP as a method to get there.

Click to expand...

It is most definitely not a LOP thread, been doing that for years.

It is specifically about a BMP at take off power, 85% or so.

Back to BMP

The theory of heat flash causing near siezure as suggested by the ECI paper is interesting but it would seem to me that we would have far more broken engines as evidence if it were that simple.

I can come up with circustances that are far more aggravating and common than BMP when it comes to abruptly increasing heat flux to the piston with a relatively cold cylinder. Advancing the throttle on take off, advancing the throttle after a long throttle off descent in cold air, and for that matter, the normal Lycoming-recommended leaning procedure.

It would seem that the APS folks woould have seen something amiss in the thousands of pulls they have done ona highly instrumented and inspected engine.

Here is the link

http://www.sportaviationonline.org/sportaviation/201210/#pg30

I should have posted it sooner. it's what this thread is all about.

I have read the APS pages and think its great info. I have not however noted any information on non boosted 360's. I think there could be significant differences between boosted and non boosted engines as well as items on individual engines such as piston squirters when looking at heat transfer. I would love to see some data on a stock io360 trying these techniques on a test stand. For the moment the ECI experience is all I have found.

George

N427EF said:

It is specifically about a BMP at take off power, 85% or so.

Click to expand...

Let's note that the 25"/2200 data dump in the first post is 65~70% for an IO540, not 85%. For an IO-360 angle valve it would be about 65%. There is nothing about that chart to suggest all is well at 85%.

I bring up the IO-360 because it is the only engine for which we seem to have some actual detonation data. The one scenario which might swell a piston very rapidly is detonation; heat transfer to the combustion chamber surfaces spikes upward instantly when the boundary layer gets blown away.

The ECI bulletin says they were doing a mixture pull for a detonation test at a "rich cruise power setting", but they don't tell us the actual MP and RPM. They also say they didn't record evidence of detonation. As such, I will not claim detonation was the root of their problem....but I will point out it could become your problem.

This is an IO-360 chart for 2200 RPM and a whopping 28.8" MP. The power line says 140, about 70%. In mixture sweep from bog rich to very lean, there is only the slightest hint of detonation:



However, a BMP at 2400 RPM and 28.8 could be risky. Look close at the detonation zone, then look close at the EGT values. Pulling to 50 LOP at this power setting would leave you parked within the detonation zone (about the 56 lbs/hr point at the bottom of the chart). This is about 87% power:



To be realistic, not many of us will set 5 notches oversquare at sea level WOT and do a Big Mixture Pull. However, you might be inclined to do one at a manifold pressure typical for having climbed clear of the pattern, 27" and 2700.....and you would be fine, at about 92% power:



Here's the point(s).....

Percent power is a lousy way to express do and don't ops.

That said, you can probably do a BMP at any setting below 65%, and 70% doesn't look unreasonable based on the data available. When in doubt, higher power settings should probably be undersquare for a BMP. Yeah, I know what they say about running the big Continentals, which brings us to....

The above charts are for a specific engine. I can't prove it, but I am perfectly wiling to assume that nothing specific transfers to another engine model or brand.

The manufacturers are entirely capable of supplying the raw data we need to make educated decisions, but they won't do it. Neither does APS, who only gives us the red box.

The 2400/28.8 chart nicely illustrates that you may not be able to pull lean enough to avoid a problem at some power settings. At the same time it illustrates why you want to pull through the near-peak and peak zone as quickly as you can if you've selected a pro-detonation MP/RPM combination. Dawdling in that detonation zone at some higher percentage power setting may be bad for your pistons.

And one last thing.....if you have plenty of cooling, why bother reducing RPM, doing a BMP, and climbing LOP? You're way back on HP, so the climb takes a lot longer. Sure, fuel flow is less, but total fuel used isn't very different. The full power, mixture for best power climb gets you pushed over in cruise sooner and further on toward the destination in less time. Want to save fuel? The data above says if you must do a BMP it is better to keep RPM up. Look at the 27/2700 chart. A BMP to 50 LOP reduces fuel flow to 61 lbs/hr from nearly 85 lbs/hr at 150 ROP with a loss of only 12 horsepower. You save fuel and keep most of the climb rate.

Thanks Dan

I think I have the answer I was looking for based on your charts and
elaborate details in the previous post.

I should have been more precise about what part of my chart I wanted opinions on but just to be sure it was the take off part with 83% power,2400 RPM and 28.00 MAP is where I did a BMP. Unfortunately the chart looses interactive properties by posting a snap shot and I failed to position the vertical yellow line in the right place.
Here it is ther same chart one more time, cropped to show the important part as well as the precise numbers at the time of the BMP.
Probably best to save the BMP for cruise settings.

Doing the Big Mixture Pull is all about getting from the full rich zone, over to a LOP setting of some sort, without spending large amounts of time in a detonation possible zone. This is not as much a problem on a NA engine as it is a TC or TN engine.

LOP climbs do work in both NA and TC/TN engines however, they really are only of significant benefit in a turbocharged engine. The problem is those who do not have a good understanding of what they are doing can make a mess of LOP climbs on turbocharged engines and for that reason alone, George, Walter and John do not actively promote them outside their APS live course....simply because if you do them wrong, you will shorten the life of your engine.

For all the NA engines, mostly the sort in RV's there is little value in doing LOP climbs, the time and distance flown Vs fuel use is negligible and not worth it. So in short, while you can do them, don't bother.

The best practice for all NA climbs is to ensure correct fuel flow at sea level ISA (HP rating / 10) in USGPH, take note of EGT going through 700-1000 AMSL, and every couple of thousand lean back to that target EGT. If climbing beyond 10,000 you may want to chase the extra few ponies and less fuel flow and climb around 75f ROP and this will give you the best climb performance and clean up those cylinders a bit.

I did a bunch of climb tests a little while back for George's interest, and took video and with the full data set, it was absolute proof that the best method of any, and I did them all, was the Target EGT method. Time to climb, distance to climb, CHT's everything was in your favour. Doing full rich to 5000, or 25/2500 or LOP did nothing good.

Ernst, I noticed you were worried about high EGT's...... mate that is not a worry at all, no such problem, except for TIT, but you knew that all along

The ECi article

That article is brimming with pony pooh! Rapid leaning.....cylinder rapidly heating..... no data as to what they did, or what they found, just the creation of some more urban myths and old wives tales. If that were real, automotive engines would be failing all over the place.

Rapid leaning as per a BMP could not heat the piston like that anyway, and in fact on a turbo engine the very reason for doing a BMP is to avoid the Peak Pressure climbing high and close to TDC.....that is the whole point.

If any of you have been to the Carl Goulet Memorial Engine Test Facility, and seen these things done on several engine types, Lycoming and TCM, you would quickly understand that this ECi article is someones poor explanation for a failure they did not understand, or wanted to cover up. In which case why would they print it?

It is interesting to note that the OWT's and rubbish from TCM and Lycoming seemed to start appearing at a great rate of knots after the departure of folk like Carl Goulet. I am sure this is not a coincidence.

By the way, those of you who have ever considered taking the APS course, I see that for this week only (up to Friday 23rd) John Deakin will give you a $100 credit if you do the fun test and then choose to take the online course. This new fun test is aimed at getting people to recognise they do not know what they don't know, and is a great way to have a :toe dipped in the water".

Can I suggest that when you create a user name to do the fun test, use your name followed by VAF, to show that your VAF community as in different to all the others. Mr Deakin is always interested to know where folk come from and the info is not of any other use.

I might start a whole new thread for this....... It is a great offer!